High-voltage power supply regulation



Dec. 4, 1951 v. J. DUKE 2,577,112

HIGH-VOLTAGE POWER SUPPLY REGULATION Filed April 9, 1948 77 iff INVENTORB M @ATTORNEY Patented Dec. 4, 1951 HIGH-VOLTAGE POWER SUPPLY REGULATIONVernon J. Duke, Rockville Centre, N. Y., assigner to Radio Corporationof America, a corporation of Delaware Application April 9, 1948, SerialNo. 19,963

1 Claim.

lThis invention is directed to electronic apparatus and particularly totelevision apparatus of the electronic variety. In the electronicapparatus for television transmission and reception, it is commonpractice to utilize cathode ray type tubes which employ the use of anelectron beam which is caused to scan a target structure within anevacuated chamber. This electron beam is usually formed by an electrongun structure which denes the cross-sectional dimension of the beam andfocuses it (by electrostatic or electromagnetic fields) upon the` targetstructure with a current intensity which is primarily a function of thegrid-cathode bias potential. The cathode ray beam velocity is determinedby the accelerating potentials applied to the beam acceleratingelectrodes. In accordance with this latter requirement it is necessaryto provide some source of relatively high D. C. potential in the orderof several thousand volts which is applied to the acceleratingelectrodes of the particular type of cathode ray tube employed. Thesehigh voltage supplies may take several forms, but to date, economicaland practical construction of such suppliesV usually results in a powersupply having poor voltage regulation with respect to load demands.

Defective operation of television systems due to poor regulationcharacteristics of accelerating electrode high voltage supplies is mostvividly apparent in the operation of kinescopes used in the reproductionof television pictures. It is Well known that in the operation of thekinescope that should the high voltage accelerating potential applied tothe beam vary in magnitude during electromagnetic or electrostaticdeflection of the beam the extent of the angular deflection of the beamwill also vary due to the change in deflection sensitivity accompanyingthe change in accelerating potential. Since the electron beam current inmany cases constitutes the sole load upon the accelerating potentialpower supply, any variations in electron beam current Vdue to modulationof this electron beam by signals applied4 to the kinescope willreilectzavarying load upon the accelerating potential power supply. Accordingly,if the power supply does not have good voltage regulationcharacteristics with respect to load, the angular deection of the beamwill vary with the signal variation of beam current. Also it is to benoted -that the focus of the electron beam upon the fluorescent screenof a television kinescope or like type of cathode ray tube is a functionof the accelerating potential applied to the target and therefore ifthis accelerating potential is caused to changeas the electron beamtraverses the raster area, a variation in the line denition of theraster will necessarily result from the consequent change in focus ofthe electron beam.

The aforementioned effects of accelerating potential regulation ondeflection sensitivity and proper focusing in a television kinescopetype of tube is particularly noticeable in television receiversdeveloping the necessary high voltage for the kinescope reproducing tubefrom a separate R. F. type power supply or a pulse type power supplyassociated with the horizontal deflection circuit. Although these typesof power supplies are well constructed at considerable expense, it iswell known that the inherent voltage regulation of such supplies isgenerally poor. Accordingly, this poor regulation commonly results inthe reproduction of television pictures having variable dimensionsdependent upon average beam current which in turn corresponds to thebackground level of television picture.

It is therefore the purpose of this invention to provide a methodwhereby the undesirable eiects of poor voltage regulation in highvoltage power supplies used as a source of accelerating potential forcathode ray type tubes can be substantially eliminated with need oflittle additional equipment and cost.

It is further a purpose of this invention vto provide a method ofcontrolling the magnitude of the output voltage of a high voltagegenerator used to supply electron beam accelerating potential totelevision kinescope type tubes in such a way as to obviate the changesin raster size and beam focus caused by poor regulation of the highvoltage power supply.

It is further an object of this invention to provide the apparatusnecessary to economically alter existing electronic equipment employinghigh voltage acceleration of electron streams such that improvements inperformance may be realized through the elimination of inadequateaccelerating power supply regulation characteristics. I

A further purpose of this invention resides in the provision of themethod and apparatus which may be applied to television receivers whicheliminates change in raster size as produced upon the kinescope due tochanges in background level of the video signal as may be present insystems having pulse type or R. F. type power supplies for the supply ofsaid kinescope accelerating electrodes, these types of power suppliesnormally having inherently poor regulation characteristics.

The novel features which are believed to be characteristic of myinvention are set forth in the appended claim. The invention itself,however, as to both its organization and method of operation, will bestbe understood through reference of the following description, especiallywhen considered in connection with the accompanving drawings wherein:

Figure 1 shows an embodiment of the invention;

Figure 2 shows another embodiment of the invention.

Referring now to the accompanying drawing there is shown in Fig. l myinvention as applied to a typical pulse type high voltage power supplyas adapted to provide accelerating potential for television typekinescopes. The electron tube I has its plate element I2 connected tothe low irnpedance winding of an auto-transformer I4 through which platesupply potential is supplied from source IB. The screen grid I8 ofelectron .tube I 0 is also connected to the positive potential source I3through dropping resistor 2G which eiects a reduction in voltage appliedto the screen element I3 under that of the full positive power ysupplypotential I5. In accordance with the operation of this unit which willlater be described,

thecontrol grid 22 of the electron tube Ie may be supplied with a seriesof pulses 24 which are ca- .pacitively coupled through condenser 26. Acon- ,trol grid return resistor 28 is shown connected from grid 22 toground. Suitable bias for the grid 22 may be obtained by means ofcathode dropping resistor 29.

'I'he high impedance end 3B of the auto-transformer winding I4 isconnected to plate 32 of rectifier tube 34 which has its cathode 35kconnected through bleeder resistor 38 to ground. Also con- .nected`from the cathode 36 Yto ground is ilter capacitor` 4U which serves as afilter and storage capacitor for the rectifying tube 34. The cathode 35is further connected to the high voltage accelerating terminal 32 of thekinescope 44 in a conventional manner. The focusing electrode 48 of "thekinescope is connected to a tap 4B .on high voltage bleeder l38 and the-rst anode-electrode 50 supplied with a suitable positive voltagenecessary for the proper operation of the kinescope.

a conventional manner the control grid 52 of the kinescope 44 issupplied with a video signal V54 which has its D. C. component restoredthrough .a suitable form of a D. C. restoration circuit 'indicathodecurrent of kinescope 44 is adapted to proyduce a voltage drop acrosstapped resistor 6I placed in yseries 4with Athe circuit .from thekinescope cathode 62 and ground.

u The voltage drop appearing across a portionof dropping resistor 6I inthe cathode circuitof the lkinescope is appliedthrough an isolatingresistor 7l] vto the grid 'F2 of electron tube 14. Capacitor "T6 isconnected from the control grid 72 to ground vand provides an R. C. timeVdelay network `in cooperation wthres'istor 10. Ampler 'tubelll opcratesin conjunction with amplifier tube I8 as a cascaded cathodefollower-grounded grid type of D. C. amplifier. Grid 80 of electron tube'i8 is supplied with a suitable positive D. C. potential @2 t0 permitoperation of the tube on a proper portion of its transfer characteristiccurve and is required because of the somewhat larger voltage dropusually app-earing across the common cathode load resistor 84 which isconnected to the cathode 86 and B8 of the electron tubes 7S, i4respectively.

The operation of the pulse type power supply shown in Fig. l so as toproduce a high voltage D. C. source conforms to common usage in everyrespect. The amplier tube It) in its unexcited state is `allowed .topass a nominal plate current whose magnitude is established by the valueof self bias imposed by cathode resistor 29 in combination with theValue of screen voltage applied to screen grid I8. This plate currentnecessarily passes through the low impedance winding 4of theauto-transformer I4 to the B supply terminal IB. The controlV grid ofthe amplifier tube EE is supplied with a series of. pulses 24 which haveSullicient amplitude in the negative direction to establish platecurrent cutoff in the vacuum tube I during the durations of the morenegative e'xtents of the pulses. Since plate current is permitted to owduring the positive extents of the signal 24 this sharp transition fromplate current to no plate current 4in the inductive winding ofauto-transformer I4 produces a transient having a relatively steep wavefront. This is, in effect, equivalent tothe sudden stoppage of currentthrough an inductance which, according to well known principles, causesa rise in voltage across the terminals of such an inductance which isproportional to the inductance and to the rate of change in the currentthrough the 'inductance Hence, the vacuum tube I0 operates as a form ofswitch which is given an equivalent high rate of action or short openingtime throughl the steepness of the pulse contours applied to its controlgrid. Typical circuits operating with a B supply voltage intheneighborhood of two' or three hundred volts may, during the platecurrentcutoi cycle ofthe tube ID, produce transient voltages in the order ofseveral thousand volts on Athe plate` I2 of the vacuum tube I3. It isevident that during the transient occurring in the low impedance primaryof the auto-transformer I4,

that additional voltage will be induced inthe 'iier tube 34 to ground isthe sum of the'self'in- *or more, whereas the B power supply potentialvmay be only two to three hundrd" volts. Necesl-sarily the voltagetransients appearingl across the entirety of the auto-'transformerlwilllbe facting across 'a resonant'circuit `comprisedorltlie inductanceof the entire transforrner'fw-inding Y in parallel with the strayvcapacity'eiecti-Vely across its terminals. Thus, the transients-inducedthrough the ampliiier tube I 0 inthe autotransformer will tend Ltodevelop a series 'of damped waves having the above'irecited high voltageamplitude. Rectifier tube '34 is soco'nnected to rectify the Apositiveportion-oi. these damped wave 'trains and thereby produce across "I51bleecer resistor as ahig'h D. o. vonage which may v images.

SCOPE.

` to the beam current oi the kinescope.

" be in the order of several thousand volts or more.

Filter capacitor 40 connected from the cathode 3B to ground of theVacuum tube 34 reduces the amount of ripple due to the periodicity ofthe control pulses applied to the grid 22 or the vacuum tube l0.

The magnitud-e of the voltage appearing across the bleeder resistor 38of course can be controlled by the value of the screen potential appliedto the vacuum tube I0, since proper selection of the screen potentialwill permit the tube to operate on different portions of its platecurrent characteristics and hence impart different r-ates of currentchange to the primary I4 of the autotransformer for a given pulsecontour applied to the tube control grid.

With the above operation in mind which successively produces a highvoltage D. C. potential of a magnitude suitable for application to ahigh voltage accelerating electrode 42 of a kinescope, such as 44, it isevident that should it be desired to adjust the value of the highvoltage so applied, it will be necessary only to establish a control ofthe magnitude of the D. C. volta-ge applied to the screen grid I8 of thevacuum tube I0. The kinescope 44 is shown in Fig. l to be conventionallyconnected in a manner which would be useful in the reproduction oftelevision Focusing electrode 45 of the kinescope is supplied with theproper high voltage potential by means of tap 48 on high voltage bleeder38.

The first anode potential of the kinescope may be `applied to rst anode50 -by connection to the common B supply for the equipment, whilecontrol grid 52 is supplied with a video signal 54 through the D. C.restorer circuit 56. For simplicity in illustration, deflection meansfor the kinescope are not shown since they are not functional in theoperation of this invention.

As before pointed out, the control grid 52 of the kinescope 44 isconnected to permit its placement at variable negative D. C. potentialsbelow ground which is derived from supply source 60 through tap 58 onpotentiometer 59. This control establishes the background level for thepicture reproduced by the tube and serves as the commonly knownbrightness control for the kine- As before noted, in series with thecathode S2 and ground is placed series potentiometer 6| which isprovided with an adjustable arm E3. Since the cathode current of mod-ernkinescopes consists almost entirely of the electron beam currentproduced by the electron gun the voltage drop across potentiometer 6|will be proportional Thus, as the kinescope beam current increasesthereby imposing a varying load upon the high voltage system and causingthe accelerating potential applied to electrode 42 to lower in value dueto the inherent poor regulation of such a supply, cornpensation for suchincrease beam current may be lmade by increasing the value of the screenpotential of amplier tube l0. This may be automatically accomplished bymeans of the control tubes 14 and '18 having the following action:

As the beam current increases the potential between potentiometer tap 53Vand ground increases in a positive direction and, through isolatingresistor 10, this potential increase is applied to the control grid 12of vacuum tube 14. Vacuum tube 14 is seen to be connected as a cathodefollower type of amplifier and therefore its cathode 86 also becomesmore positive with respect to ground. This increase in voltage fromcathode to ground is imposed upon the input circuit of amplifier tube 16by merit of the cathode impedance 84 ycommon to the two tubes. Groundedgrid amplier 18 is shown to have its grid 80 placed at a positivepotential with respect to ground by a voltage source 82. This positivevalue of bias subtracts from the negative 'bias imposed on the grid 80by merit of the voltage drop across cathode resistor 84 which isestablished mainly by the plate current of vacuum tube 14. Thus, thetube 18 may be operated on a portion of its characteristics such that anincrease in cathode potential occasioned by a positive swing of itscathode 88 will cause the plate current through dropping resistorsubstantially to decrease. This decrease in plate current 'I8 will causethe IR drop across resistor 20 to decrease and thereby increase thevoltage effective at the screen I0 of ampliiier tube l0. As heretoforede- Y scribed, this increase in screen voltage will cause the highvoltage output appearing across electrode 42 and'ground to increase. Itis seen therefore by proper adjustment of potentiometer tap 63 thecircuit may be made to operate so that the poor regulationcharacteristics of the power supply may be compensated by the increasein screen voltage caused by the amplified version of the voltage dropacross a selected portion of resistor 5|. Condenser 'H5 cooperates withthe resistor 10 to form a time delay network which may be desirable toprevent the regulating system from 4responding to instantaneous changesin kinescope cathode current. The value of this time constant maybeadjusted to suit individual needs and circumstances.

The embodiment of my invention shown in Fig. 2 is similar in operationto the arrangement shown in Fig. 1. However, in Fig. 2 my invention isshown applied to a high voltage supply of the R. F. type such asdescribed, for example, in a U. S. Patent No. 2,374,781, to Schade,dated May l, 1945. The power amplier tube 90 is operated as aself-excited oscillator by means of plate coil 92 which is disposed toexcite the grid tickler coil 94 and cause sustained oscillation of ythecircuit. A high impedance winding 96 is placed in mutually inductiverelationship with primary winding 92 so as to produce a high voltageacross the plate 98 of vacuum tube rectier |00 having its cathode |02connected to ground through high voltage bleeder resistor |04. Thefrequency of the oscillator may be adjusted by means of variablecapacitor 93 which is used to tune the primary `92 (oscillator tankcircuit) of the R. F. transformer. Detailed operation of this circuit isdescribed fully in the aforementioned patent to Schade. It is sufficientto note in connection with the present invention that the value of thepotential applied to the screen grid |04 of vacuum tube 90 elTectscontrol of the voltage to ground appearing across the plate 98 of vacuumtube |00. This action follows by merit of vacuum tube 90 being operatedas a class C oscillator wherein plate current iiows for only a portionof the entire period of oscillation. As in `the previous embodiment thekinescope |06 has a high voltage accelerating potential applied to itsaccelerating electrode |08 from this high voltage power supply whosenormal regulation characteristics are inherently and undesirably poor.The kinescope |06 is provided with a brightness control H0 and a cathodedropping resistor potentiometer ||2 which has tap H4. The voltageappearing across tap I4 and ground which is proportional to the cathodecurrent of the kinescope |06 is applied through resistor I6 to thecontrol grid H8 of vacuum tube |20. As here- :grid |04 vof oscillator4tube 90.

their entire ranges.

'fitopre explained, .in `.connecfwrl `with Fig. 1, this iD. voltageapplied to the control ygrid H8 .causes a change in the potentialapplied-www@ Accordingly, as .the beam current through -the kinescope|04 increases, the Fcontrol grid `I I 8 is caused to swing morepositively which, in turn, obtains a reduc- .tion in the plate currentvof vacuum vtube Y|22. kThis plate current reduction causes vthe voltagedrop vacross plate resistor ,|24 to decrease, ,thereby 'increasing thevoltage applied to thescreen |04. This increase in screen potential then:causes ran increase .of ,energy to be 'applied tothe high voltagesystem which is sufficient to vcause the voltage across the acceleratingelectrode 1,08 zto ground to remain substantially constant relgardlessof kinescope 'beam current changes. Again the degree of compensation maybe adjusted by positioning of potentiometer tap |14 non Apotentiometer II2 and suitable .delay action may vbe incurred through the section ofthe -time vconstant vof .condenser H1 and isolating resistor H6.

' VI have Jfound that jin the proper adjustment of my invention asapplied to the ygeneral forms above described, -it is most expeditiousto adjust the taps 63 and Vlid on .control potentiyometers 60 and 'H2vrespectively (shown in Figs.

1 and 2) while repeatedly adjusting the brightness cntrols'59 and H0respectively throughout The aforementioned adjustments are mader whileWatching the raster produced on the television kinescope screen. TheAdegree Vof high Voltage power supply compensation -control isestablished at a level which will maintain the 4raster size constant-for all settings of the brightness control. Although this adjustvmentprocedure is only useful in applications of tential with respect tobrightness control setting for conditions vwhen .the voltmeter wasremoved.

While I have `illustrated two embodiments of my invention in connectionwith television kinescopes employing electrostatic focusing, othermodifications and applications will readily occur tothose skilled in theart. I do :not therefore devsiremy invention to lbe limited to theparticular embodiments illustrated and described `and 1.52011,-v,template by the appended claim to cover-fall modifications which fallWithin the-spirit `andscope of my invention.

What I claim as new and desire to-secureby Letters Patent of the U. S.is:

Cathode ray tube apparatus comprising .a

'cathode ray tube, l.a space dischargetube having va cathode, Yan anode,a control electrode and .la ,screen electrode, means for .supplyingpulses .to saidcontrol electrode for periodically.biasing said tube tocutoff, an autotransiormer, the `anode circuit of said tube including aportion of the ,winding vof said autotransformer, Va rectifier having acathode and an anode, a connection-from said autotransformer to `A'theanode of said rectiiier, a connection from said rectifier cathode-to vanelectrode of said cathode -ray tube, -an yelec-- tron-emitting electrodein said cathode ray tube, an impedance in circuit with said electronemitting electrode, a direct current amplifier, a connection from vsaidimpedance `for controlling Asaid direct cur-rent amplifier, a controltube hav- REFERENCES CITED The following references are of record in thefile of this patent:

UNITED STATES PATENTS Number Name Date 2,122,990 Pooh July 5, l19382,173,221 Ballard Sept. 19, 1939 2,219,194 Mynall Oct. 22, 19402,255,485 Dome Sept. 9, 1941 2,265,620 Bahring Dec. 9, r1941 2,302,876Malling Nov. 24, 1942 2,371,897 Knick Mar. 20, 1945 2,443,030 FosterJune 8, 1948

